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Our days are getting longer as the moon slowly drifts away from the Earth

A recent study exploring the Earth’s ancient association with the moon has revealed that days on our planet are gradually getting longer, largely due to changes in the distance between the Earth and the moon. 

Shorter days of the past

According to the experts, about 1.4 billion years in the past, a day on Earth lasted just over 18 hours, a phenomenon caused by the moon’s closer proximity, which influenced Earth’s rotational behavior.

“As the moon moves away, the Earth is like a spinning figure skater who slows down as they stretch their arms out,” explained study co-author Stephen Meyers, a professor of Geoscience at the University of Wisconsin-Madison.


To help them understand and describe this peculiar phenomenon, the researchers developed a statistical technique bridging astronomical theories and geological findings, called astrochronology. 

This method offers insights into Earth’s ancient geology, solar system evolution, and old climate transitions captured in rock formations.

“One of our ambitions was to use astrochronology to tell time in the most distant past, to develop very ancient geological time scales. We want to be able to study rocks that are billions of years old in a way that is comparable to how we study modern geologic processes,” Meyers said.

Milankovitch cycles 

The gravitational pull from other celestial bodies, such as the planets and the moon, impacts Earth’s movement in space, resulting in variations in our planet’s axial rotation, wobble, and solar orbit. 

These shifts, known as Milankovitch cycles, play a role in sunlight distribution on Earth and consequently, our climate patterns, which can be observed in the rock record, spanning hundreds of millions of years.

Solar system chaos 

However, diving deeper into billions of years of Earth’s history presents significant challenges. While traditional methods such as radioisotope dating lack the precision needed to identify these cycles, limited knowledge about the moon’s history and the concept of solar system chaos – first introduced by Jacques Laskar in 1989 – further complicates matters.

The solar system, with its myriad components including planets circling the sun, is susceptible to solar system chaos, meaning that even minor initial variations can lead to significant alterations millions of years later, a phenomenon posing major challenges to understanding long-term changes.

However, in 2022, Meyers and his colleagues managed to crack the code on this chaotic solar system in an examination of sediments from a 90 million-year-old rock formation which captured the Earth’s climate cycles. 

Projecting backward 

Yet, the further back in the rock record scientists are trying to go, the less reliable their findings tend to be.

For instance, the moon is now moving away from the Earth at a rate of 3.82 centimeters annually. 

According to Meyers, using this current rate and projecting backward, it follows that “beyond about 1.5 billion years ago, the moon would have been close enough that its gravitational interactions with the Earth would have ripped the moon apart.” However, this contradicts the known age of the moon, which is 4.5 billion years.

Focus of the study 

To solve this puzzle, Meyers aimed to accurately track the movements of our neighboring planets billions of years back to fathom their effects on Earth and its Milankovitch cycles. He presented this dilemma at Columbia University’s Lamont-Doherty Earth Observatory during his sabbatical in 2016.

Alberto Malinverno, a researcher at Columbia and co-author of the recent study, was present. “I was sitting there when I said to myself, ‘I think I know how to do it! Let’s get together!’” he recounted. “It was exciting because, in a way, you dream of this all the time; it was a solution looking for a problem.”

How the research was conducted 

During their collaboration, they combined a statistical approach Meyers devised in 2015, termed TimeOpt, with astronomical theories, geologic insights, and a refined statistical method called Bayesian inversion, to help them understand system uncertainties.

Testing their new method, named TimeOptMCMC, they examined two rock strata: the 1.4 billion-year-old Xiamaling Formation in Northern China and a 55 million-year-old segment from the Walvis Ridge in the southern Atlantic. 

Reliable evaluations 

This technique allowed for reliable evaluations of Earth’s rotational axis direction and orbital shape from both recent and ancient times, and factored in uncertainties, while also helping them pinpoint the day’s length and the gap between Earth and the moon.

“In the future, we want to expand the work into different intervals of geologic time,” Malinverno said.

Two other studies have also employed rock records and Milankovitch cycles to decode Earth’s history and behavior. One team at Lamont-Doherty authenticated Earth’s orbital fluctuations using an Arizonian rock formation. Another collaborative effort involving Meyers studied marine organisms’ evolution and extinction cycles, tracing back 450 million years.

“The geologic record is an astronomical observatory for the early solar system. We are observing its consistent rhythm, preserved in rocks and life’s history,” Meyers concluded.

More about the moon’s impact on Earth

The Moon, Earth’s only natural satellite, has long captured our imagination. But beyond its romantic allure, the Moon actively shapes our world in a myriad of tangible ways.

Tidal Forces: The Ebb and Flow

First and foremost, the Moon affects Earth’s oceans through gravitational forces. As the Moon orbits our planet, its gravitational pull tugs at the Earth’s water, leading to the phenomenon we recognize as tides.

The water bulges toward the Moon, creating high tides on the side facing the Moon and, due to centrifugal forces from Earth’s rotation, on the opposite side as well. Consequently, locations between these bulges experience low tides. The tides rise and fall twice a day in most coastal areas due to this intricate dance between the Earth and the Moon.

Stabilizing Earth’s Wobble

The Moon also plays a pivotal role in stabilizing Earth’s axial tilt. Earth’s axis tilts at an angle, which gives us our seasons. Without the Moon’s gravitational influence, Earth might experience dramatic variations in its axial tilt, causing extreme and unpredictable changes in climate.

The Moon’s presence ensures our planet’s tilt remains relatively constant at around 23.5 degrees, providing a stable climate that has been crucial for the development and survival of life.

Lunar Eclipses: Shadows in the Sky

The relationship between the Earth and Moon also provides a visual spectacle: lunar eclipses. These occur when Earth passes directly between the Sun and the Moon, casting a shadow on the Moon’s surface. During a total lunar eclipse, the Earth’s umbra (central shadow) covers the Moon, often giving it a reddish hue due to the Earth’s atmosphere bending sunlight and indirectly illuminating the Moon.

Impact on Earth’s Length of Day

As mentioned in this article, the Moon’s gravitational pull also causes a slight braking effect on Earth’s rotation. This effect, known as tidal friction, results in a gradual lengthening of our day. Over millions of years, the Earth’s rotation has been slowing down, and days have been getting longer, albeit at a very gradual pace.

In summary, the Moon does more than just light up our night skies. It shapes the rhythms of our oceans, stabilizes our climate, showcases celestial phenomena, and even impacts the length of our days. In this delicate cosmic balance, the Moon remains an influential and essential partner to Earth.

The study is published in the journal Proceedings of the National Academy of Sciences.

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